1. Field of the Invention
The present invention relates to an optical device wafer processing method.
2. Description of the Related Art
An optical device wafer is composed of a substrate such as a sapphire substrate or a SiC substrate and a semiconductor layer (epitaxial layer) of gallium nitride (GaN), for example, formed on the front side of the substrate. A plurality of optical devices such as LEDs are formed in the semiconductor layer so as to be partitioned by a plurality of crossing streets (division lines). This optical device wafer has a relatively high Mohs hardness and it is therefore difficult to divide the wafer by using a cutting blade. Accordingly, a laser beam is applied to the wafer along the division lines to divide the wafer into the individual optical devices, which are used for electrical equipment such as mobile phones and personal computers.
As a method of dividing the optical device wafer into the individual optical devices by using a laser beam, the following first and second processing methods are known in the art. The first processing method includes the steps of applying a laser beam having an absorption wavelength (e.g., 355 nm) to the substrate of the wafer to an area corresponding to the division lines to thereby form an ablated groove along each division line and next applying an external force to the division lines to thereby divide the wafer into the individual optical devices (see Japanese Patent Laid-Open No. Hei 10-305420, for example).
The second processing method includes the steps of applying a laser beam having a transmission wavelength (e.g., 1064 nm) to the substrate of the wafer along the division lines in the condition where the focal point of the laser beam is set inside the substrate in an area corresponding to the division lines, thereby forming a modified layer inside the substrate along each division line and next applying an external force to the division lines to thereby divide the wafer into the individual optical devices (see Japanese Patent No. 3408805, for example). According to these processing methods, the optical device wafer can be reliably divided into the individual optical devices.